In the past there has been extensive description in the patent and other technical literature relating to electrophoretic migration imaging processes and colorants useful therein. For example, a description of such processes and colorants may be found in sugarman, U.S. Pat. No. 2,758,939, issued Aug. 14, 1956; Kaprelian U.S. Pat. No. 2,940,847; 3,100,426; 3,140,175 and 3,143,508; Tulagin et al. U.S. Pat. Nos. 3,384,565; 3,384,488 and 3,615,558; Clark U.S. Pat. No. 3,384,566; and Yeh U.S. Pat. No. 3,383,993. In addition to the foregoing patent literature directed to conventional photoelectrophoretic migration imaging processes another type of electrophoretic migration imaging process which advantageously provides for image reversal is described in Groner U.S. patent application Ser. No. 607,650, filed Aug. 25, 1975.
However, regardless of the particular electrophoretic migration imaging process employed, an essential component of any such process is the electrically photosensitive particles. And, of course, to obtain an easy-to-read, visible image it is important that these electrically photosensitive particles be colored as well as electrically photosensitive. Accordingly, as is apparent from the technical literature regarding electrophoretic migration imaging processes, work has been carried on in the past and is continuing to find colorants which possess useful levels of electrical photosensitivity and which exhibit good colorant properties. Thus, for example, various types of electrically photosensitive materials are disclosed for use in electrophoretic migration imaging processes, for example, in Sugarman U.S. Pat. No. 2,758,939; Kaprelian U.S. Pat. No. 2,940,847, Tulagin et al. U.S. Pat. No. 3,384,488 and U.S. Pat. No. 3,615,558 noted hereinabove.
In large part, the art, to date, has generally selected useful electrically photosensitive or photoconductive pigment materials for electrophoretic migration imaging from known classes of photoconductive materials which may be employed in conventional photoconductive elements, e.g., photoconductive plates, drums, or webs used in electrophotographic office copier devices. For example, both Sugarman and Kaprelian in the above-referenced patents state that electrically photosensitive materials useful in electrophoretic migration imaging processes may be selected from known classes of photoconductive materials. And, the phthalocyanine pigments described as a useful electrically photosensitive material for electrophoretic imaging processes in Tulagin et al. U.S. Pat. No. 3,615,558 have long been known to exhibit useful photoconductive properties.
It is recognized, as set forth above, that many useful electrically photosensitive materials which are employed in electrophoretic migration imaging processes can be and have been selected from known photoconductive materials. However, in accord with the present invention, a class of electrically photosensitive materials has been discovered which is believed to represent a new class of materials. In this regard, it is noted that Jones, Jr. et al. U.S. Pat. No. 3,562,248, issued Feb. 9, 1971, describe certain bisazo pigments derived from couplers obtained by condensing 8-amino-2-napnthols with dicarboxylic acid chlorides and the use of such pigments in electrophoretic imaging systems. These bisazo pigments differ structurally from the pigments of the present invention.
Various other azo compounds that are structurally different from the pigments of the present invention, including azo compounds containing naphthyl groups, and that have been found useful in electrophoretic imaging systems, are described in the following patents: U.S. Pat. Nos. 3,652,438 and 3,852,208; British Pat. Nos. 1,146,142; 1,160,671; 1,340,207 and 1,348,121.